Fix v0.8.8 demo transcript overflow on mobile

[aryamthecodebreaker]

Summary

• prevents long generated transcript code from expanding the mobile document
• allows transcript code blocks to scroll horizontally within their own bounded container
• keeps the documentation grid item shrinkable at narrow widths

Verification

• npm ci (0 vulnerabilities)
• web lint
• production web build (all 11 static routes/assets)
• real browser at 390×844: viewport 390px, document scroll width 390px, body scroll width 390px
• visual screenshot and console smoke in dark mode